No, I did spot that quite quickly, and set the VS to 100bpm. I tried altering the VS bpm but it only has 0.1bpm increments. The MV is finer - 0.01bpm, and as I posted, if I set the MV to 100.05bpm it's a lot closer after 4 minutes.
If I use the Master (MV) transport controls, or alter the bar-beat-tick setting by hand, the Slave (VS) immediately jumps into perfect alignment. That sort of implies to me that there is NO ongoing sync, and that it's just the MMC Play/etc commands that are being received.
For sure, there's no other visual sign that the two machines are in sync.
As I say, I'm a syncing newbie, so I'm scrabbling a bit.
(I'm about to go on holiday but will check back for advice - I appreciate your help, guys)